Energy scavenging sensors which operate by harvesting energy from its ambient environment are useful for long-term sensing applications where the use of batteries (rechargeable or non-rechargeable) is considered to be impractical. Depending on the level of ambient energy that is available, the sensor can implement different functionalities that range from complex signal-processing to wirelessly transmitting data to an external radio-receiver. FIG. 1 shows a typical range of scavengeable power and different sensor functionalities that can be achieved at these power levels. For instance, the self-powered sensor which was reported in “An asynchronous analog self-powered cmos sensor-data-logger with a 13.56 mhz rf programming interface”, C. Huang et al can scavange nanowatts of power from ambient strain variations and can compute and store the statistics of the strain-signal. As the scavengeable power level is increased, the stored statistics can be wirelessly transmitted, as shown in FIG. 1.
However, a major limitation of remotely powered sensor (e.g. using strain variations or using RF) is that events being monitored by the sensor cannot be time-stamped. This is because the sensor does not have access to a system timer or clock that is continuously active for the entire monitoring period. For a typical structural health monitoring application, the monitoring period could easily span more than 20 years. One method to achieve continuous powering is to scavenge energy from perennial sources of power like ambient thermal-noise, as illustrated in FIG. 1. Also shown in FIG. 1 is that the typical power-level of ambient-thermal-noise≈10−18W, which is challenging for operating conventional electronic devices. In this regards, biology serves as a motivation providing several examples where many biochemical computations (e.g. for DNA hybridization) are driven by thermal-noise and in many instances the computations are robust to variations in ambient temperature. Thermally-driven and diffusion-based information processing was also proposed by Charles Bennett as a way to approach fundamental limits of computation (in terms of energy-efficiency).
Therefore, there is a need for a self-powered timer that is driven by thermal processes and thermal energy.
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